1. Field of the Invention
The present invention relates to a photocathode applicable to detection or measurement of light having a predetermined wavelength, and an electron tube equipped with the same.
2. Related Background Art
As a material for a photocathode which is sensitive to ultraviolet rays having a wavelength not longer than 200 nm, cesium iodide (CsI), which is a semiconductor, has been well known, for example. This photocathode has a quantum efficiency of about 25%, at the maximum, for photoelectric conversion in the vacuum ultraviolet region. Since this photocathode dramatically decreases its level (quantum efficiency for photoelectric conversion) with respect to the light to be detected having a wavelength not shorter than 200 nm, it has been known as a so-called solar-blind photocathode which is insensitive to solar light.
Accordingly, such a solar-blind photocathode is often employed in a so-called electron tube (phototube equipped with a photocathode) such as photomultiplier and is used for detecting or measuring weak light in the ultraviolet region.